This invention relates to a shim structure for sound dampening brake squeal noise in a disc brake apparatus.
This invention relates particularly to a shim structure which includes a sheet of shim material and a continuous layer of an adhesive on one, inner surface only of the sheet of shim material. The adhesive adheres the shim structure to a steel backing plate. The backing plate has a friction pad structure mounted on the other side of the steel backing plate.
My U.S. Pat. No. 5,518,088 issued May 21, 1996 discloses several embodiments of a shim structure having a sheet of aluminum and a continuous membrane of a high temperature acrylic adhesive which is on one surface only of the sheet of aluminum and which adheres the shim structure to a steel backing plate. This U.S. Pat. No. 5,518,088 is incorporated by reference in this application.
Aluminum is the preferred silencer material, but the present invention will also work for shim structures which use aluminum, metal alloys, laminates of metals and other materials, or plastic silencers. The shim structure is constructed of silencer materials which have vibratory characteristics sufficiently different from the vibratory characteristics of the steel backing plate so as to effectively dampen the noise or squeal which could otherwise be produced during braking operation.
In disc brake apparatus a rotatable disc rotates with the axle of a wheel to be braked. Two friction pad structures are disposed on opposite sides of the disc. Each friction pad structure comprises a steel backing and a brake pad. The friction pad structures are moved inwardly, toward one another, under the force supplied by a hydraulically actuated piston and related caliper fingers of a caliper mounting structure. The plates are moved outwardly, away from one another, by return springs.
When the piston and caliper fingers press the backing plates inwardly, the inner surfaces of the braking pads are engaged in frictional, braking contact with the disc.
A relatively high pitched and undesired brake squeal noise can be produced during such braking engagement of the pads on the disc.
The brake squeal noise is produced by vibration of the friction pad structures during braking actuation.
To reduce and/or to eliminate the undesired brake squeal noise, sound dampening shim constructions have been used, both by original equipment manufacturers and by brake repair shops.
The sound dampening shim constructions have been positioned both between the hydraulically actuated piston and the piston engaging surface of the related steel backing plate and also between the caliper fingers and the caliper contact surface of the related steel backing plate.
As the thickness of the metal component of the shim structure is increased, and as metals heavier than aluminum are used in the silencer, there is a risk that the silencer may dislodge in service. The force of the rotating of the brake disc, as transmitted into the friction pad structure, can cause a torque or twisting force to be imposed on the shim structure by the related piston and caliper elements of the disc brake apparatus so as to produce a shear force in the adhesive of the shim structure. Under the extreme conditions of heat and vibration incurred in the disc brake apparatus, the adhesive may tend to crystallize; or the adhesive may not, by itself, be sufficient to prevent dislodging of the shim structure from the backing plate in service.
It is a primary object of the present invention to construct a friction pad and shim structure in which at least one retaining pin extends through the shim structure and into the backing plate for preventing dislodging of the shim structure in service.
It is a related object to insert the retaining pin through the shim structure and into the backing plate so that the force of the rotating action of the brake disc is at a 90.degree. angle to the retaining pin. This 90.degree. angle provides effective resistance to any shifting or rotation of the shim structure with respect to the backing plate during actuation of a disc brake apparatus.
It is another important object of the present invention to construct a retaining pin so that the retaining pin has an outer surface which is disposed substantially flush with the outer surface of the shim structure, whereby the outer surface of the retaining pin does not interfere with the positioning or functioning of an actuator piston structure, caliper structure or other disc brake structure. The flush mounting allows the system of the present invention to be used for any caliper design.
It is another object of the present invention to construct the silencer shim structure so that the shim structure can be added to the friction pad structure at the last stage of production, after painting of the friction pad structure. This enables the silencer to be graphically decorated because it is installed after the pad painting process. This has two benefits:
1) the silencer can be inexpensively decorated; and
2) the mounting process does not interfere with the pad production cycle.
It is another object of the present invention to construct a shim structure which avoids problems presented by prior shim constructions and which also has functional and marketing benefits not obtainable with prior shim constructions.